The major histocompatability complex (MHC) of mammals (H-2 in mice; HLA in humans) is a multigene family whose members encode cell-surface glycoproteins. Recently, attention has been focused on possible non-immune functions of MHC associated genes. It is known that there are one or more major genes associated with the H-2 complex that influence pre- and post- implantation development including timing of the first cleavage division, steroid receptor number and responsiveness, morphogenesis of the mandible and other facial structures and overall fetal growth and survival. Variation in all of these traits is related to variation in H-2 haplotype. Given this, we will (a) morphometrically analyze the relationship between H-2 haplotype and the characteristic changes (e.g. linear, angular, and area dimensions) in craniofacial growth of congenic mice 13 - 17 days of gestation, (b) determine the existence of maternal effects (genotypic, cytoplasmic, etc.) and (c) determine the proportion of the total phenotypic variation among congenic strains that is due to environmental variation. Since certain teratogens (corticosteroids, phenytoin) are known to disturb craniofacial development and their ability to induce such malformations is associated with H-2 haplotype, we will repeat all experiments after maternal treatment with these teratogens.